In making cord-reinforced, vulcanized rubber products, for example automobile tires, strength under stress is critical. In many instances, it is found that the bond between the cord and the rubber is the point at which tire failure occurs.
The art of bonding tire cord to rubber is very complex, however, it is generally recognized at present that the "so-called" RFL system is the most widely used method of adhering textile cords to rubber. The RFL system (see U.S. Pat. No. 3,968,295, for example) comprises a dip composition of a butadiene-styrene-vinylpyridine rubber latex and a resorcinol-formaldehyde resin. In particular, the latex usually comprises 15-20% styrene, 65-75% butadiene, and 10-15% vinyl-pyridine.
Resorcinol is a very expensive commodity which is also in short supply. Furthermore, it exhibits certain undesirable toxicological characteristics. Moreover, and most importantly, the presently used cord dip compositions containing the resorcinol-formaldehyde resins must be aged before use, and their useful lifetime, once prepared, is a matter of only a few days at best, depending on the ambient temperature at which they are stored.
Therefore, a cord dip composition in which the resorcinol-formaldehyde resin is replaced, which provides at least as good adhesion of cord to rubber as the present RFL system, at lower cost and which does not require aging would solve a long-felt need.